1. Technical Field
The present invention relates to a liquid ejecting apparatus.
2. Related Art
Ink jet printers using piezoelectric elements (for example, piezo elements) as actuators are known as ink jet printers that print images or documents by ejecting ink. The piezoelectric elements are installed to correspond to a plurality of nozzles in a head unit and are each driven according to driving signals. Accordingly, predetermined amounts of ink (liquid) are ejected from the nozzles at predetermined timings to form dots.
In such printers, high productivity is necessarily realized due to high speed and high image quality. As a technology for realizing high productivity, for example, a technology for arranging a plurality of nozzles across a larger width than a target product (printing sheet) has been proposed (see JP-A-2011-121249).
When this technology is used to attempt an improvement in productivity, many nozzles and piezoelectric elements are necessary with an increase in the resolution of a target product. In order to drive the piezoelectric elements, a relatively high voltage (for example, about 40 volts) is necessary. For this reason, it is necessary to perform power amplification on driving signals using amplifiers, and then to supply the driving signals to many piezoelectric elements simultaneously and concurrently. A class D amplification circuit which is smaller in power loss and is miniaturized more easily than analog power amplification of class AB has been proposed as such an amplifier (see JP-A-2007-168172).
Specifically, the class D amplification circuit supplying driving signals to the piezoelectric elements is configured such that original signals which are sources of driving signals are pulse-modified by a modulation circuit to generate modulated signals, the modulated signals are subjected to digital amplification (class D amplification) to generate amplified modulated signals, and the amplified modulated signals are smoothed by a lowpass filter to output the amplified modulated signals as the driving signals.
A piezoelectric element is a capacitive load such as a capacitor from the viewpoint of electricity. For this reason, when the plurality of piezoelectric elements are driven, load characteristics vary according to the number of driven piezoelectric elements. Therefore, a technology for providing a plurality of feedback circuits with different frequency characteristics and selecting and switching the feedback circuits according to the number of piezoelectric elements to be driven in a configuration in which driving signals are feedback for class D amplification has been proposed (see JP-A-2011-224784).
Incidentally, in the class D amplification, there is a demand for monitoring the driving signals as in the feedback circuits. The driving signals are signals obtained by smoothing the amplified modulated signals subjected to class D amplification by a lowpass filter. However, the driving signals are not completely smoothed and ripples remain. For this reason, there is a problem in that it is difficult to accurately obtain the voltages of signals to be monitored.